The invention relates to devices for washing magnetic particles. More particularly, the invention relates to devices for washing magnetic particles in conjunction with a magnetic bottom pull.
A suspension of magnetic particles coated with antibodies or other binding reagents may be employed as a versatile solid phase for separating a variety of soluble or suspendable entities, including various analytes, antigens, and cells. After a suspension of magnetic particles has bound its target entity, the application of a magnetic field causes the magnetic particles to migrate to the area of greatest field density. This process is called magnetic sedimentation. The magnetic particles form a pellet in the area of greatest magnetic field density. As the magnetic particles sediment toward a pellet, they carry their target entities with them.
One protocol for magnetic separation employs a test tube rack having a magnet positioned at the bottom. The magnet is oriented so that, when test tubes are inserted into the rack, the magnetic particles magnetically sediment to the bottom of the tube. This orientation of magnet is called a bottom pull. After the magnetic particles have formed a pellet, the test tube rack is inverted so as to cause the liquid phase to decant from the test tubes. During the decanting process, the pellet of magnetic particles is retained within the test tube by magnetic attraction. After the liquid is decanted, wash liquid may be pipetted into the test tube. The test tube is then vortexed in order to resuspend the magnetic particles into the wash liquid. After the vortexing, the test tube may be reinserted into the magnetic rack so as to cause the resuspended magnetic particles to magnetically sediment a second time. After the magnetic particles have pelleted, the wash liquid may be decanted so as to complete one wash cycle. Further wash cycles may be performed as required.
Since the magnet is relatively heavy, the process of tilting the rack when decanting the test tube can be somewhat cumbersome. Also, since each test tube must be vortexed manually, the resuspension process can become somewhat tedious. Accordingly, what is desired is a method for evacuating the test tube without tilting the rack and for resuspending the magnetic particles without vortexing or removing the test tubes from the magnetic rack.